Collision avoidance radar for trains is pregnant for safety transportation. In order to realize low cost and high performance of azimuth accuracy, we have developed MMW (Milli-Meter Wave) radar, which employs switched phased array and frequency stepped technology. This paper analyses the radiation patterns of transmitting/receiving antennas and compensation method for amplitude/phase errors of synthetic wideband frequency stepped signal. To confirm the operation of the radar, low cost millimeter-wave collision avoidance radar was fabricated. Lots of experiments confirmed a high azimuth and range resolution.